Block copolymer elastomer catheter balloons

ABSTRACT

Balloons for medical devices, particularly balloon angioplasty catheters, are made from particular block copolymer thermoplastic elastomers in which the block copolymer is made up of hard segments of a polyester or polyamide and soft segments of polyether; the polyester hard segments are polyesters of an aromatic dicarboxylic acid and a C 2  -C 4  diol; the polyamide hard segments are polyamides of C 6  or higher carboxylic acids and C 6  or higher organic diamines or of C 6  or higher aliphatic ω-amino-α-acids, and the polyether soft segments are polyethers of C 2  -C 10 , diols; the block copolymer has a low flexural modulus, namely less than 150,000 psi; the block copolymer has a hardness, Shore D scale, of greater than 60; and the percentage by weight of the block polymer attributable to the hard segments is between about 50% and about 95%. The polymers provide high strength, thin wall, compliant and semi-compliant balloons, which leads to a low profile catheter. The low profile catheters have very good initial crossing, good trackability, good recrossing after first inflation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 08/671,681filed Jun. 28, 1996 now abandoned, which is a continuation of U.S.application Ser. No. 08/397,837, filed Mar. 2, 1995 now U.S. Pat. No.5,556,383, which is a continuation-in-part of U.S. application Ser. No.08/204,554, filed Mar. 2, 1994, now abandoned.

BACKGROUND OF THE INVENTION

Balloons mounted on the distal ends of catheters are widely used inmedical treatment. The balloon may be used widen a vessel into which thecatheter is inserted or to force open a blocked vessel. The requirementsfor strength and size of the balloons vary widely depending on theballoon's intended use and the vessel size into which the catheter isinserted. Perhaps the most demanding applications for such balloons arein balloon angioplasty in which catheters are inserted for longdistances into extremely small vessels and used to open stenoses ofblood vessels by balloon inflation. These applications require extremelythin walled high strength relatively inelastic balloons of predictableinflation properties. Thin walls are necessary because the balloon'swall and waist thicknesses limit the minimum diameter of the distal endof the catheter and therefore determine the limits on vessel sizetreatable by the method and the ease of passage of the catheter throughthe vascular system. High strength is necessary because the balloon isused to push open a stenosis and so the thin wall must not burst underthe high internal pressures necessary to accomplish this task. Theballoon must have some elasticity so that the inflated diameter can becontrolled, so as to allow the surgeon to vary the balloon's diameter asrequired to treat individual lesions, but that elasticity must berelatively low so that the diameter is easily controllable. Smallvariations in pressure must not cause wide variation in diameter.

While angioplasty balloons are considered inelastic relative to balloonsused in most other applications, there is in the art a generalclassification of such balloons based on their expandability or"compliance" relative to each other. As used herein, "non-compliant"balloons are the least elastic, increasing in diameter about 2-7%,typically about 5%, as the balloon is pressurized from a inflationpressure of about 6 atm to a pressure of about 12 atm, that is, theyhave a "distension" over that pressure range of about 5%."Semi-compliant" balloons have somewhat greater distensions, generally7-16% and typically 10-12% over the same pressurization range."Compliant" balloons are still more distensible, having distensionsgenerally in the range of 16-40% and typically about 21% over the samepressure range. Maximum distensions, i.e. distension from nominaldiameter to burst, of various balloon materials may be significantlyhigher than the distension percentages discussed above because wallstrengths, and thus burst pressures, vary widely between balloonmaterials. The 6-12 atm inflation range is used in the presentapplication to allow direct comparison of the compliance attributes ofvarious balloons.

The strength of the polymer materials used in the balloons varieswidely. The strongest balloons are also the most inelastic, being madeof highly orientable polymers such as polypropylene, polyethyleneterephthalate or other phthalate polyesters or copolyesters, and nylons.Tensile wall strengths are commonly 20,000-50,000 psi. Commercialangioplasty balloons made of such materials with nominal diameters inthe range of 1.5-4.5 mm have distensions in the non-compliant tosemi-compliant range and can often be rated to pressures of 16 atm orhigher without risk of bursting (actual burst pressures may exceed 20atm). Generally, however, as compliance increases the wall strengthdecreases. Other semi-compliant and compliant balloons are made of lesshighly orientable polymers such as ethylene-vinyl acetate, polyvinylchloride, olefin copolymers and ionomer resins. The wall strengths ofballoons made from these less orientable materials are still lower thanthose made from the highly orientable polymers, commonly in the range of6,000-15,000 psi, resulting in lower rated maximum inflation pressuresof 9-10 atm.

The particular distension and maximum pressure attributes of a balloonare also influenced both by polymer type and by the conditions underwhich the balloon is blown. Angioplasty balloons are conventionally madeby blowing a tube of polymer material at a temperature above its glasstransition temperature. For any given balloon material, there will be arange of distensions achievable depending on the conditions chosen forthe blowing of the balloon.

In U.S. Pat. No. 4,906,244 to Pinchuck there are described balloons ofnylon (i.e. aliphatic polyamide) materials, such as nylon 12, nylon 11,nylon 9, nylon 6/9 and nylon 6/6. Like all other polymer materials thedistensions of these balloons can be determined, within a range, bycontrolling blowing conditions such as initial dimensions of tubing,prestretching, hoop ratio and heat set conditions. The data in thereference show that compliance characteristics can be obtained rangingfrom non-compliant to semi-compliant characteristics and that wallstrengths of greater than 15,000 can be obtained. The reference suggeststhat higher compliances can be achieved with nylon materials but thereis no indication of what other nylons or other balloon formingconditions could be employed to do so.

It has also been suggested to prepare balloons of thermoplasticelastomers in U.S. Pat. No. 4,254,774 to Boretos, and polyamideelastomers have been mentioned among a number of possible balloonmaterials suggested in U.S. Pat. No. 5,250,069 to Nobuyoshi, et al, butthere are many of such thermoplastic elastomer polymers and before theinvention hereof it has been expected that performance of balloons madefrom these materials would not be generally any better than high tointermediate compliance made from conventional thermoplastic polymerssuch as polyethylene ionomer, polyvinyl chloride, polyethylene orethylene-vinyl acetate.

In U.S. Pat. No. 5,290,306 polyester ethers and polyetheresteramidepolymers of Shore D hardness less than 55 have been proposed for use asa sleeve or co-extruded outer layer to a balloon of a biaxially orientednylon or polyethylene terephthalate (PET) material, so as to provide theballoon with improved softness and pin-hole and abrasion resistance.

Polyurethane block copolymers having flexural modulus of about 190,000and an ultimate elongation of 250% are disclosed as balloon materials inEP 0592885 and mention is made of also using polyester block copolymersor polyamide block copolymers but no suggestion is made that suchalternative copolymers could be usefully employed if their flexuralmodulus was substantially lower or their ultimate elongation wassubstantially higher than the disclosed polyurethane block copolymers.

SUMMARY OF THE INVENTION

New balloon materials, which possess a unique combination of physicalproperties including non-compliant, semi-compliant and compliantdistension attributes, good flexibility and high tensile strength, aremade from particular block copolymer thermoplastic elastomerscharacterized as follows:

the block copolymer is made up of hard segments of a polyester orpolyamide and soft segments of polyether;

the polyester hard segments are polyesters of an aromatic dicarboxylicacid and a C₂ -C₄ diol,

the polyamide hard segments are polyamides of C₆ or higher, preferablyC₁₀ -C₁₂, carboxylic acids and C₆ or higher, preferably C₁₀ -C₁₂,organic diamines or of C₆ or higher, preferably C₁₀ -C₁₂, aliphaticω-amino-α-acids, and

the polyether soft segments are polyethers of C₂ -C₁₀, preferably C₄ -C₆diols;

the block copolymer has a low flexural modulus, namely less than 150,000psi, preferably less than 120,000 psi;

the block copolymer has a hardness, Shore D scale, of greater than 60;and

the percentage by weight of the block polymer attributable to the hardsegments is between about 50% and about 95%.

From such polymers, balloons having compliant to semi-compliantexpansion profiles can be prepared with wall strengths greater than15,000 psi, frequently greater than 20,000 psi. The high strength of theballoons produced from the polymers allows for construction of lowprofile catheters and the low flexural modulus contributes to a softerfeel found with the balloons of the invention, compared to those made ofother high strength polymer materials. Low profile catheters made withthe inventive balloons have very good initial crossing, goodtrackability and good recrossing after first inflation.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the distension from nominal diameter to burst ofseveral balloons of the invention prepared from a polyamide/polyetherpolyester block copolymer using different hoop ratios to form theballoon.

FIG. 2 is a graph as in FIG. I using an alternate polyamide/polyetherpolyester block copolymer to form the balloon of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The preferred balloons of the invention are made of polyamide/polyetherblock copolymers. The polyamide/polyether block copolymers are commonlyidentified by the acronym PEBA (polyether block amide). The polyamideand polyether segments of these block copolymers may be linked throughamide linkages, however, most preferred are ester linked segmentedpolymers, i.e. polyamide/polyether polyesters. Such polyamide/polyether/polyester block copolymers are made by a molten state polycondensationreaction of a dicarboxylic polyamide and a polyetlier diol. The resultis a short chain polyester made up of blocks of polyamide and polyether.The polyamide and polyether blocks are not miscible. Thus the materialsare characterized by a two phase structure: one is a thermoplasticregion that is primarily polyamide and the other is elastomer regionthat is rich in polyether. The polyamide segments are semicrystalline atroom temperature. The generalized chemical formula for these polyesterpolymers may be represented by the following formula: ##STR1## in whichPA is a polyamide segment, PE is a polyether segment and the repeatingnumber n is between 5 and 10.

The polyamide segments are suitably aliphatic polyamides, such as nylons12, 11, 9, 6, 6/12, 6/11, 6/9, or 6/6. Most preferably they are nylon 12segments. The polyamide segments may also be based on aromaticpolyamides but in such case significantly lower compliancecharacteristics are to be expected. The polyamide segments arerelatively low molecular weight, generally within the range of500-8,000, ore preferably 2,000-6,000, most preferably about3,000-5,000.

The polyether segments are aliphatic polyethers having at least 2 and nomore than 10 linear saturated aliphatic carbon atoms between etherlinkages. More preferably the ether segments have 4-6 carbons betweenether linkages, and most preferably they are poly(tetramethylene ether)segments. Examples of other polyethers which may be employed in place ofthe preferred tetramethylene ether segments include polyethylene glycol,polypropylene glycol, poly(pentamethylene ether) and poly(hexamethyleneether). The hydrocarbon portions of the polyether may be optionallybranched. An example is the polyether of 2-ethylhexane diol. Generallysuch branches will contain no more than two carbon atoms. The molecularweight of the polyether segments is suitably between about 400 and2,500, preferably between 650 and 1000.

The weight ratio of polyamide to polyether in the polyamide/polyetherpolyesters used in the invention desirably should be in the range of50/50 to 95/5, preferably between 60/30 and 92/08, more preferably,between 70/30 and 90110.

Polyamide/polyether polyesters are sold commercially under the PEBAXtrademark by Atochem North America, Inc., Philadelphia Pa. Examples ofsuitable commercially available polymers are the Pebax® 33 seriespolymers with hardness 60 and above, Shore D scale, especially Pebax®7033 and 6333. These polymers are made up of nylon 12 segments andpoly(tetramethylene ether) segments in about 90/10 and about 80/20weight ratios, respectively. The average molecular weight of theindividual segments of nylon 12 is in the range of about 3,000-5,000grams/mole and of the poly(tetramethylene ether) segments are in theranges of about 750-1,250 for the 6333 polymer and about 500-800 for the7033 polymer. The inherent viscosities of these polymers are in therange of 1.33 to 1.50 dl/g.

Generally speaking, balloons of Pebax® 7033 type polymer exhibitborderline non-compliant to semi-compliant behavior and balloons ofPebax® 6333 type polymer show semi-compliant to compliant distensionbehavior, depending on the balloon forming conditions.

While the Pebax®-type polyamide/polyether polyesters are most preferred,it is also possible to use other PEBA polymers with the physicalproperties specified herein and obtain similar compliance, strength andsoftness characteristics in the finished balloon.

As an alternative to polyamide elastomers, it is also possible toutilize polyester/polyether segmented block copolymers and obtainsimilar balloon properties. Such polymers are made up of at least twopolyester and at least two polyether segments. The polyether segmentsare the same as previously described for the polyamide/polyether blockcopolymers useful in the invention. The polyester segments arepolyesters of an aromatic dicarboxylic acid and a two to four carbondiol.

Suitable dicarboxylic acids used to prepare the polyester segments ofthe polyester/polyether block copolymers are ortho-, meta- or para-phthalic acid, napthalenedicarboxylic acid ormeta-terphenyl-4,4'-dicarboxylic acids.

Preferred polyester/polyether block copolymers are poly(butyleneterephthalate)-block-poly(tetramethylene oxide) polymers such as ArnitelEM 740, sold by DSM Engineering Plastics. Hytrel polymers, sold byDuPont which meet the physical and chemical specifications set outherein can also be used, but are less preferred.

It is believed important that the block copolymers have a hardness,Shore D scale, of at least 60 and a flexural modulus of no more thanabout 150,000, in order to obtain the desirable combination of strength,compliance and softness characteristics which distinguish the inventiveballoons. Preferably the Shore D hardness is in the range of 65-75 andthe flexural modulus is in the range of 50,000-120,000. The preferredpolymers useful in the invention are also characterized by a highultimate elongation of about 300% or higher and an ultimate tensilestrength of at least 6,000 psi.

The balloons of the invention are made using known techniques forforming catheter balloons. For coronary angioplasty catheter balloons(balloon diameters of about 1.5-4.0 mm), single wall thicknesses of lessthan 0.001 inches, preferably less than 0.0007 inches, are readilyobtained. Wall strengths for such balloons are in excess of 15,000,typically at least 18,000 psi, and in most cases in the range of about20,000 to 32,000 psi. For peripheral angioplasty, balloons of up to 10mm diameter may be used and in such cases somewhat thicker walls may beemployed. Even with a 10 mm balloon, wall thicknesses of about 0.0015 mmor less can be employed to provide balloons with burst pressures of atleast 10 atm. Suitably the balloons are formed by expansion of tubing ata hoop ratio (mold diameter/tubing ID) of between 3 and 8, preferablybetween 4 and 7.

The following examples illustrate the preparation and unique propertiesof balloons of the invention.

EXAMPLES

TUBING EXTRUSION:

In examples 1-9, 11, and 13 all tubing materials were made from AtochemPebax® 7033 and Pebax® 6333 by extrusion. Polymer pellets were dried toless than 0.10 wt % moisture content before extrusion. Tubing wasextruded at melt temperature range of 200° C. to 220° C. by hotfeedthroat through seven extruder zones with controlled temperatures.The extrusion conditions were based upon manufacturer's recommendedpolymer processing conditions. After the polymer material extruded outof the die in tube form it passed through a small air gap and was cooledin a deionized water bath maintained at about 65° F. A puller was usedto pull the tube through the water bath. After passing through thepuller, the extruded tubing was cut into 8 inch sections or spooled. Avariety of tubing sizes were made by this method.

Example 1

The product of this example is a 2.25 mm balloon made from Pebax® 7033.This polymer has a Shore D hardness of 69, a flexural modulus of 67,000,an ultimate tensile strength of 8,300 psi and an ultimate elongation of400%. The tubing sections had an OD of 0.0270 inch and an ID of 0.0179inch. In order to form a 2.25 mm balloon with a 20 mm body length, amold having dimensions that allowed the tube to blow out to theappropriate body size and balloon waist inner diameters was used.

After the tubing section was securely inside the mold, the mold wasplaced in a holder. The tubing section extended out the top of the moldand was fed into a Touhy clamp through which nitrogen gas applied to theinner lumen of the tubing at 280 psi with tension applied to the tubing.The tubing section at the bottom of the mold was clamped off such thatthe pressure was maintained inside the tubing section. The mold was thengradually dipped into a deionized hot water bath maintained at 90° C.(±1° C.) to a point just above the proximal waist portion of the mold ata controlled manner. A balloon was formed by radial expansion withinternal pressure using a hoop ratio of 5.1. After the balloon formed,the mold was removed from the hot water bath and cooled forapproximately 10 sec in a deionized water bath maintained at about 10°C.

Balloons prepared in this manner were subjected to standard burst testsby measuring the double wall thickness of the deflated balloon,inflating the balloon at incrementally increasing pressures andmeasuring the outside diameter at each increment until the balloonburst. Burst strength, distension and balloon wall strength werecalculated from the data obtained. Average results are given in Table 1.

Example 2

The product of this example is a 3.00 mm balloon made from Pebax® 7033.The tubing sections had an OD of 0.0290 inch and an ID of 0.0179 inch. A3.00 mm size mold was used to produce the balloons. These 3.00 mmballoons were made by the same procedure used in example 1, except forthe water bath temperature and internal blowing pressure. The water bathtemperature and the pressure were maintained at 95° C. and 300 psi,respectively. The hoop ratio of the balloon was 6.2. The results oftesting for burst, distension and wall strength are also listed in Table1.

Example 3

The product of this example is a 3.00 mm balloon made from Pebax® 7033.The tubing sections had an OD of 0.0316 inch and an ID of 0.0179 inch. Acorresponding size mold was used to mold balloons. In this example, 90°C. water bath and 400 psi internal blowing pressure were used. The testresults provided in Table 1 show that these balloons gave a higher burstpressure than the previous examples.

Example 4

The product of this example is a 3.00 mm balloon made from Pebax® 7033.The tubing sections had an OD of 0.0320 inch and an ID of 0.0215 inch. A3.00 mm size mold was used to produce the balloons. The same moldingconditions described in example 2 were used except that the tubing wasprestretched at room temperature before molding balloons. The prestretchstretching ratio X was 1.5 in this example. The test results of thisexample are listed in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Burst and Distension Test Results of Pebax ® 7033 Material (averages      of at least 5 balloons).                                                                 Single Wall                                                                         Burst                                                                             Distension                                                                          Distension                                                                          Distension                                                                          Wall                                        Balloon Size                                                                        Thickness                                                                           Pressure                                                                          88 psi-Burst                                                                        88 psi-132                                                                          88 psi-176                                                                          Strength                               Example                                                                            (mm)  (inch)                                                                              (psi)                                                                             (%)   psi (%)                                                                             psi (%)                                                                             (psi)                                  __________________________________________________________________________    1    2.25  0.00042                                                                             230 21.3  4.2   10.9  25400                                  2    3.00  0.00047                                                                             230 12.7  3.2   7.1   29200                                  3    3.00  0.00060                                                                             260 12.8  3.6   6.9   25900                                  4    3.00  0.00049                                                                             220 23.5  4.4   9.0   26300                                  __________________________________________________________________________

Example 5

Balloons having 2.0-3.0 mm diameters were prepared from Pebax® 7033using hoop ratios of 4.6, 5.1 and 6.7. The balloons were expandedincrementally at 37° C. until they burst. The results, plotted in FIG.1, show semi-compliant curves with very high burst strengths rangingfrom 15-18 atm and maximum distensions at burst of 24%-45%.

EXAMPLE 6

In this example, balloons were made from Pebax® 6333. This polymer has aShore D hardness of 63, a flexural modulus of 49,000, an ultimatetensile strength of 8,100 psi and an ultimate elongation of 300%. Thesame balloon forming procedure as in example 1 was used, except as notedbelow. The product of this example is a 2.5 mm balloon. The tubingsections had an OD of 0.0316 inch and an ID of 0.0179 inch. A 2.5 mmsize mold was used to produce the balloons. In this example, a 95° C.water bath and a 300 psi internal blowing pressure were used. The hoopratio for blowing the balloon was 5.5. The results of burst, distensionand wall strength are shown in Table 2.

Example 7

Pebax® 6333 tubing with an OD of 0.0310 inch and an ID of 0.0170 inchwas used to produce 3.0 mm balloon. The water bath temperature was 90°C. and the internal blow pressure was 300 psi. The hoop ratio forblowing the balloon was 6.9. Test results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Burst and Distension Test Results of Pebax ® 6333 Material (averages      of at least five balloons).                                                              Single Wall                                                                         Burst                                                                             Distension                                                                          Distension                                                                          Distension                                                                          Wall                                        Balloon Size                                                                        Thickness                                                                           Pressure                                                                          88 psi-Burst                                                                        88 psi-132                                                                          88 psi-176                                                                          Strength                               Example                                                                            (mm)  (inch)                                                                              (psi)                                                                             (%)   psi (%)                                                                             psi (%)                                                                             (psi)                                  __________________________________________________________________________    6    2.50  0.00058                                                                             220 33.7  3.4   17.4  19900                                  7    3.00  0.00049                                                                             210 17.1  4.2    9.7  26100                                  __________________________________________________________________________

Example 8

Balloons having 2.25-3.0 mm diameters were prepared from Pebax® 6333using hoop ratios of 4.2, 5.5 and 6.9. The balloons were expandedincrementally at 37° C. until they burst. The results, plotted in FIG.2, show semi-compliant and compliant curves with burst strengths of11.5-14 atm and distensions at burst of 23%-69%.

Example 9

The products of this example were 3.00 mm balloons made from Pebax®6333. The tubing sections had an OD of 0.0350 inch and an ID of 0.0190inch. A 3.00 mm size mold was used to produce the balloons. Portions ofthe tubing sections were prestretched at a stretching ratio of 2 (λ=2)before molding the balloons. The prestretched portions were on eitherside of a central 8 mm unstretched portion protected during theprestretching operation by a clamp. The unstretched central portion wasthen formed into a 20 mm long, 3.0 mm diameter balloon body by expansionunder pressure in a mold as in the previous examples. The temperature ofthe water bath was 95° C. and the expansion pressure was 340 psi. Theballoons made in this manner had a hoop ratio of 6.2, a single body wallthickness of between 0.0006 and 0.0007 inches, a distal waist wallthickness of between 0.0014 and 0.0021 inches a proximal waist wallthickness of between 0.0014 and 0.0018 inches. The burst pressure of theballoons was about 270 psi. The balloon distension was semi-compliant.

Example 10

The material used in this example was Arnitel EM 740 sold by DSMEngineering Plastics. This polymer had a Shore hardness of 74D, aflexural modulus 120,000 psi, an ultimate tensile strength of 6,400 psiand an ultimate elongation of 340%. 2.25 mm Balloons were prepared fromtubing of dimensions OD=0.0270 inches and ID=0.0179 inches. The tubingwas necked at two ends and the balloon body portion was unstretched, asdescribed in Example 9. The molding temperature was 80° C. The moldingpressure was 290 psi. The molding tension was 50 grams. Balloonproperties are given in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Burst and Distension Test Results of Arnitel EM 740 Material                  __________________________________________________________________________               Single Wall                                                                         Burst                                                                             Distension                                                                          Distension                                                                          Distension                                                                          Wall                                        Balloon Size                                                                        Thickness                                                                           Pressure                                                                          88-Burst                                                                            88-132                                                                              88-176                                                                              Strength                               Example                                                                            (mm)  (inch)                                                                              (psi)                                                                             %     %     %     (psi)                                  __________________________________________________________________________    11   2.25  0.00041                                                                             238 34    6.2   16.7  25,700                                 __________________________________________________________________________

Example 11

The material used in this example was Pebax 7033. The moldingtemperature was 95° C. The molding pressure was 500 psi. 2.00 mmBalloons were prepared from tubing segments as set forth below. Alltubing segments were stretched at room temperature with differentstretching ratios and starting tubing dimensions. The unit of ID and ODis inches.

    ______________________________________                                        a:       the tubing was stretched at λ = 2.5 stretching ratio                 starting ID = 0.0130,                                                                              OD = 0.0252                                              ending   ID = 0.0087,                                                                              OD = 0.0177                                       b:       the tubing was stretched a λ = 3.0 stretching ratio                  starting ID = 0.0132,                                                                              OD = 0.0252                                              ending   ID = 0.0081,                                                                              OD = 0.0162                                       c:       the tubing was stretched at λ = 4.5 stretching ratio                 starting ID = 0.0132,                                                                              OD = 0.0262                                              ending   ID = 0.0064,                                                                              OD = 0.0136                                       ______________________________________                                    

The properties of the resulting balloons are set forth in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Burst and Distension Test Results of Pebax 7033 Material                                 Single Wall                                                                         Burst                                                                             Distension                                                                          Distension                                                                          Distension                                                                          Wall                                        Balloon Size                                                                        Thickness                                                                           Pressure                                                                          88-Burst                                                                            88-132                                                                              88-176                                                                              Strength                               Example                                                                            (mm)  (inch)                                                                              (psi)                                                                             (%)   (%)   (%)   (psi)                                  __________________________________________________________________________    12a  2.0   0.00058                                                                             279 14.6  4.0   6.5   18,900                                 12b  2.0   0.00060                                                                             279 14.6  3.5   6.6   18,300                                 12c  2.0   0.00062                                                                             353 22.2  3.0   5.4   22,600                                 __________________________________________________________________________

Example 12

The material used in this example was Arnitel EM 740 poly(butyleneterephthalate-block-poly(tetramethylene oxide). 2.75 mm Balloons wereprepared from tubing of dimensions: OD=0.0390 inches and ID=0.0230inches. The tubing was stretched at room temperature at λ=4.8. Thedimension of stretched tube was: OD=0.0250 inches and ID=0.0200 inches.The molding temperature was 80° C. The molding pressure was 490 psi. Themolding tension was 30 grams. The properties of the resulting balloonsare set forth in Table 5.

                                      TABLE 5                                     __________________________________________________________________________    Burst and Distension Test Results of Arnitel EM 740 Material                  __________________________________________________________________________               Single Wall                                                                         Burst                                                                             Distension                                                                          Distension                                                                          Distension                                                                          Wall                                        Balloon Size                                                                        Thickness                                                                           Pressure                                                                          88-Burst                                                                            88-132                                                                              88-176                                                                              Strength                               Example                                                                            (mm)  (inch)                                                                              (psi)                                                                             %     %     %     (psi)                                  __________________________________________________________________________    13   2.75  0.00066                                                                             265 43.9  8.0   18.2  21.700                                 __________________________________________________________________________

EXAMPLE 13

Pebax 7033 tubes with dimensions 0.0198 inch OD and 0.0339 inch ID isdrawn at room temperature with a central region protected by an insertedhypo tube approximately 0.018 inch in diameter and 1.0 inch in length.The tube was drawn until an 8 mm central region remained undrawn. Tensterilized balloons (3.0 mm in diameter and 20 mm in length) with anaverage double wall thickness 0.00142 inch are made by radiallyexpanding the 8 mm central tubing portion at 95° C. The resulting burstpressure is 270-280 psi and the distension is 9% over the range 88-176psi and 16% over the range 88-235 psi.

COMPARATIVE EXAMPLES Comparative Examples A-C

The material used in this example was Pebax 3533. This polymer has aShore D hardness of 35 and a flexural modulus of 2,800. Balloons weremade by expanding tubes of ID=0.0330 inch and OD=0.0480 inch. Themolding temperature was 66° C. The molding pressure was 80 psi.Distension and burst were run at room temperature (22° C.). Balloonproperties are set forth in Table 6.

                  TABLE 6                                                         ______________________________________                                        Burst and Distention Test Results of Pebax 3533 Material                              Balloon Single Wall                                                                             Burst  Distention                                                                           Wall                                  Comparative                                                                           Size    Thickness Pressure                                                                             10-Burst                                                                             Strength                              Example (mm)    (inch)    (psi)  %      (psi)                                 ______________________________________                                        A       1.50    0.00495   75     67     450                                   B       2.00    0.00218   50     89     900                                   C       2.50    0.00185   40     73     1060                                  ______________________________________                                    

Comparative Example D

The material used in this example was Pebax 5533. This polymer has aShore D hardness of 55 and a flexural modulus of 29,000. 3.00 mmballoons were prepared from tubing sections having an ID of 0.0190 inchand an OD of 0.0360 inch. The molding temperature was 87.5° C. Themolding pressure was 300 psi. Portions of the tubing sections wereprestretched at a stretching ratio of 2 (λ=2) before molding theballoons. The prestretched portions were on either side of an 8 mmcentral unstretched portion protected during the prestretching operationby a hypo tube as in example 13. The unstretched central portion wasthen formed into a 20 mm long, 3.0 mm diameter balloon body by expansionunder pressure in a mold. Balloon properties are set forth in Table 7.

                                      TABLE 7                                     __________________________________________________________________________    Burst and Distension Test Results of Pebax 5533 Material                      __________________________________________________________________________    Compara-                                                                           Balloon                                                                             Single Wall                                                                         Burst                                                                             Distension  Distension                                                                          Wall                                   tive Size  Thickness                                                                           Pressure                                                                          88-Burst                                                                            Distention                                                                          29.4-Burst                                                                          Strength                               Example                                                                            (mm)  (inch)                                                                              (psi)                                                                             %     88-132                                                                              %     (psi)                                  __________________________________________________________________________    D    3.00  0.00073                                                                             132 17.0  17.0  44.3  10,700                                 __________________________________________________________________________

Comparative Examples E-G

The material used in this example was Riteflex 640 poly(butyleneterephthalate-block-poly(tetramethylene oxide). This polymer has a ShoreD hardness of 40 and a flexural modulus of 12,300. Balloons were made byexpanding tubes of ID=0.0360 inch and OD=0.0430 inch. The moldingtemperature was 80° C. The molding pressure was 80 psi. Balloonproperties are set forth in Table 8.

                  TABLE 6                                                         ______________________________________                                        Burst and Distention Test Results of Riteflex 640 Material                            Balloon Single Wall                                                                             Burst  Distention                                                                           Wall                                  Comparative                                                                           Size    Thickness Pressure                                                                             10-Burst                                                                             Strength                              Example (mm)    (inch)    (psi)  %      (psi)                                 ______________________________________                                        E       1.50    0.00216   80     66     1100                                  F       1.75    0.00105   65     52     2100                                  G       2.25    0.00088   60     62     3020                                  ______________________________________                                    

What is claimed is:
 1. A balloon for a medical device formed from a length of tubing of a polymer material by radial expansion of the tubing under pressure, the polymer material comprising a block copolymer thermoplastic elastomer characterized as follows:the block copolymer comprises two or more hard segments of a polyester or polyamide and two or more soft segments of polyether;the polyester hard segments are polyesters of an aromatic dicarboxylic acid and a C₂ -C₄ diol, the polyamide hard segments are polyamides of C₆ or higher carboxylic acids and C₆ or higher organic diamines or of C₆ or higher aliphatic ω-amino-α-acids, and the polyether soft segments are polyethers of C₂ -C₁₀ diols, the block copolymer has a flexural modulus of less than about 150,000 psi; the block copolymer has a hardness, Shore D scale, of greater than 60; and the percentage by weight of the block polymer attributable to the hard segments is between about 50% and about 95%.
 2. A balloon as in claim 1 wherein the block copolymer has a Shore D hardness in the range of 65-75 and a flexural modulus in the range of 50,000-120,000 psi.
 3. A balloon as in claim 1 wherein the hard segments of the block copolymer are polyamide segments.
 4. A balloon as in claim 1 wherein said polyether segment, is selected from the group consisting of poly(tetramethylene ether), poly(pentaniethylene ether) and poly(hexamethylene ether).
 5. A balloon as in claim 1 wherein the wall strength of the balloon is at least 15,000 psi.
 6. A balloon as in claim 5 wherein the wall thickness, single wall basis, is no more than 0.0015 inches and said wall strength is greater than 18,000 psi.
 7. A balloon as in claim 6 wherein said wall thickness is no more than 0.0009 inches.
 8. A balloon as in claim 5 wherein said wall strength is greater than 20,000 psi.
 9. A balloon as in claim 1 having a compliant to semi-compliant distension profile whereby as inflation pressure is increased from 6 atm to 12 atm, the balloon expands from a nominal diameter at the 6 atm pressure to an increased diameter at the 12 atm pressure which is at least 7% greater than said nominal diameter.
 10. A balloon as in claim 9 wherein the increased diameter at 12 atm is at least 10% greater than said nominal diameter.
 11. A balloon as in claim 9 wherein the increased diameter is at least 16% greater than said nominal diameter.
 12. A balloon as in claim 9 having a nominal diameter of between 1.5 mm and 10.0 mm, the balloon having a burst pressure of at least 10 atm.
 13. A balloon as in claim 1 having a nominal diameter of between 1.5 mm and 4.0 mm, the balloon having a burst pressure of at least 12 atm.
 14. A balloon as in claim 1 wherein the hard segments of the block copolymer are polyester segments.
 15. A balloon as in claim 14 wherein said polyester segments are polyesters of an acid selected from the group consisting of ortho-, meta- or para- phthalic acid, napthalenedicarboxylic acid and meta-terphenyl-4,4'-dicarboxylic acids and a diol selected from the group consisting of ethylene glycol, 1,3-propane diol and 1,4-butane diol.
 16. A balloon as in claim 1 wherein the block copolymer is poly(butylene terephthalate-block-poly(tetramethylene oxide).
 17. A balloon as in claim 1 wherein the block copolymer is further characterized by a ultimate tensile strength of at least 6,000 psi and an ultimate elongation of at least 300%.
 18. A dilation catheter having a elongated tubular body, a balloon mounted on a distal end thereof and means for inflation of the balloon, wherein the balloon is a balloon as in claim
 1. 19. A balloon as in claim 1 wherein the tubing polymer material consists of a single polymer. 